Patent GB-954477-A (GB)
Title: Improvements in auxiliary power systems associated with aircraft gas-turbine propulsion units
Inventor: MOSS NORMAN
IPC: F02C7/32
Filed: 1959-08-20
Abstract: 954,477. Gas turbine plant. PLESSEY CO. Ltd. Aug. 8,1960 [Aug. 20,1959], No. 28448/59. Addition to 864,736. Headings F1G and F1T. [Also in Division F4] Aircraft equipment comprises an auxiliary turbine supplied with air bled from a compressor of a gas turbine propulsion unit, means being provided for supplying exhaust air from the bleed-air turbine to the pressurisation duct leading to the aircraft cabin. Further means are provided for maintaining the inlet pressure to the pressurisation duct at a predetermined multiple of the cabin pressure by automatically compensating for variations of this ratio by supplying bleed air direct to the outlet of the bleed air turbine, thus by-passing that turbine, when the pressure ratio tends to fall, and by dumping part of the bleed-air turbine discharge, thus by-passing the cabin pressurisation system, when the pressure ratio tends to increase. Air is bled from the engine compressor 18 through duct 5 to the bleed-air turbine 3, the exhaust therefrom passing through duct 2 to the pressurisation duct 1. An evacuated capsule 13 is disposed in a chamber 15 which is subject to pressure of the air turbine discharge by means of duct 16. A second evacuated capsule 18 is disposed in a second chamber 17 which is subject to pressure in the aircraft cabin by means of duct 19. A capsules are inter-connected by a rod which controls a pivoted lever 12 which in turn controls the opening of valves 10, 11 disposed in a valve chest. The system is shown in its normal position in which both valves 10, 11 are closed, the exhaust air from the turbine 3 passing to the pressurisation duct 1. Should the turbine exhaust be insufficient to maintain the desired ratio of pressure at the inlet of duct 1 to pressure in the cabin, the pressure in the chamber 17 causes the capsule 18 to be compressed, whereby the lever 12 acts to open the valve 10, so that bleed air from the duct 5 passes through the duct 7 to the pressurisation duct 1 thereby by-passing the turbine 3 and restoring the desired pressure ratio. Alternatively should the turbine supply more air than is necessary, the pressure in the valve chest 9 tends to rise and the rise in pressure is communicated to the chamber 15 via the duct 16. The capsule 13 is therefore compressed and the lever 12 causes the valve 11 to open allowing excess air to be dumped through the outlet 8. Should the air pressure in the duct 5 be insufficient to provide the required power of the turbine 3, a valve 21 is provided whereby the turbine exhaust duct 2 is opened to atmosphere. The valve 21 is mounted on the same rod as a piston 22, the lower side of which is subject to the pressure of the bleed air in the duct 5 and the upper side of which is loaded by a spring 23; a further valve 21a is carried on the same rod. Should the pressure in the duct 5 fall therefore, the valve 21 is opened and the valve 21a is closed, and bleed air still flows to the pressurisation system through by-pass duct 7 and valve 10. A non-return valve 26 may be disposed in the duct 2 either in addition or alternatively to the valve 21a.